The metals content and Conradson carbon values of a hydrocarbon feed material and particularly high boiling feeds comprising residual oils and reduced crudes are two very effective restraints on a hydrocarbon conversion operation and impose some considerable restraints in a reduced crude cracking operation with respect particularly to the catalyst regeneration operation.
The effect of increased Conradson carbon in a high boiling hydrocarbon feed material is to increase that portion of the feed converted to coke or carbonaceous material deposited on the catalyst particles. In a gas oil cracking operation, the amount of coke deposited on the catalyst is generally in the range of 4-5 weight percent of the feed. This coke deposition is attributed to four different coking mechanisms, namely, contaminant coke from adverse reactions caused by metal deposits, catalyst coke caused by acid site cracking, entrained hydrocarbons resulting from pore structure absorption, poor stripping operations and the Conradson carbon level of the feed resulting from pyrolytic distillation of hydrocarbons in the conversion zone. When processing reduced crudes there are two additional sources of coke contributed by adsorbed and absorbed high boiling hydrocarbon components which do not vaporize at the conversion conditions employed and therefore are also not removed by lower temperature stripping conditions. The second source is contributed by high molecular weight nitrogen containing hydrocarbons adsorbed on the catalyst acid sites. Thus when processing high boiling residual oils, the coke production is based on a summation of the six different methods above defined. Thus the coke production when processing reduced crudes may be estimated as approximately 4 weight percent of the feed plus the Conradson carbon value of this heavy or high boiling feed to be processed.
The catalyst thus coked is brought back to equilibrium activity by removal of deposited carbonaceous material in a regeneration zone normally in the presence of air or oxygen containing gas. The heat generated during such regeneration is removed in part by regeneration flue gas and in part by the catalyst. The regeneration temperature is normally restricted to less than 815.degree. C. or 760.degree. C. (1500.degree. F. or 1400.degree. F.) in the prior art to avoid hydrothermal deactivation of the catalyst and destruction of apparatus equipment relied upon for this purpose.
The hydrothermal stability of a zeolite catalyst is determined by the temperature and steam partial pressure at which the zeolite begins to rapidly loose its crystalline structure to yield a lower activity amorphous material. The presence of high temperature steam in the regenerator is highly undesirable and is generated by the burning of adsorbed and absorbed hydrocarbonaceous material which has a significant hydrogen content (hydrogen to carbon atomic ratios generally greater than about 0.5). Residual oils and reduced crudes comprise materials which do not vaporize at temperatures below 566.degree. C. (1050.degree. F.) but comprise materials of higher boiling points up to as high as 815.degree.-926.degree. C. (1500.degree.-1700.degree. F.) and higher of modest hydrogen content. These high boiling materials include high molecular weight materials such as prophyrins, asphaltenes and nitrogen compounds which may be basic or acidic in nature.
Thus as the end point of the feed increases above 552.degree. C. (1025.degree. F.) so does the carbon producing tendency of the feed also increase to the point that the catalyst particles accumulate heavy deposit of carbonaceous material. The present invention is directed to a method for regenerating catalyst particles comprising relatively heavy hydrocarbonaceous deposits contributed by hydrocarbon feeds of substantial Conradson carbon value.
Some prior art patents considered in the preparation of this application include the following listed patents.
______________________________________ Thomas et al 2414002 Thompson et al 2475650 Greensfelder et al 2398739 Pfeiffer et al 3563911 Jahnig et al 2434567 Gross et al 4118337 Luckenbach 4176084 Pulak 4010003 Gross et al 4057397 Vickers 4219442 Owen 3856659 Owen 3821103 ______________________________________